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August 31, 2004
Water remains safe to drink despite earthy odour in water supply
  
Works and Emergency Services reports that an earthy odour in Toronto's water
supply has become noticeable during the past few days. Taste and odour episodes
are caused by seasonal biological changes in Lake Ontario and typically occur
in the late summer or early fall. Toronto's tap water continues to be safe to
drink during these episodes.

Taste and odour episodes are caused by the presence of a naturally occurring
compound called geosmin at extremely low levels (measured in parts per
trillion) in Lake Ontario. Geosmin is not harmful to public health and the
city's water quality is not otherwise affected. Simple home remedies may be
used to reduce taste and odour in drinking water, such as keeping a jug of
water in the fridge and adding ice cubes or a few drops of lemon juice.

Two of Toronto's four water filtration plants (Island and R.C. Harris) are
permanently retrofitted with interim granular-activated carbon systems, which
reduce geosmin, but do not eliminate it entirely. The other two water
filtration plants - R. L. Clark in the west end and F. J. Horgan in the east
end - have powdered-activated carbon systems, which must be activated at the
time of a taste and odour episode. Once activated, the carbon systems in these
two plants take some time (from a few hours to a few days) for the filtered
water to reach consumers' taps.

Although it is difficult to predict when conditions will return to normal,
taste and odour episodes will generally dissipate after the lake water
temperature starts to go down (below 15 degrees Celsius).

Additional information about taste and odour episodes is available from the
Ontario Water Works Research Consortium at http://www.owwrc.com. For
information on Toronto's water and wastewater systems, residents may call Works
and Emergency Services' Water Education Line at 416-392-4546.

Media contacts:
Patrick Newland, Director, Water Supply, Works and Emergency Services,
416-392-8220
John Rudnickas, Manager, Water Quality Works and Emergency Services,
416-392-2923



 

 

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